I had the same problem and followed the above instructions with no help, but what I miss understood was not to clean anything with the cover where the paper's fed through, but on the actual glass that's under the top.
Here's what I did and it worked.
At the very front of the glass bed there should be a separate thin strip of glass that has a plastic strip over it for protection. That's the strip of glass that scans the paper fed into the scanner from the top. So what you need to do is lift the corner of the plastic, to get under it, and run a cloth or something under the plastic strip and over the glass. You can use almost anything under it to clear the glass/plastic strip. I used a moist cleaning wipe. Not a good idea because of the moisture. I could see the moisture from the wipe clinging the plastic strip to the glass after I wiped it, so I had to go under it again with on of those computer screen cleaners and everything was dry.
I scanned a blank page and the page scanned blank. Perfect!
I hope this helps.
